Personnel lifts of the pedestal type exemplified by the above patents typically have an upright mast mounted on a relatively small base member, and a work cage mounted on the mast for vertical movement.
The present invention is particularly directed to an improved construction of the vertically extendible mast of such scaffold units. For example, the mast of the U.S. Pat. No. 4,397,373 comprises a plurality of side-by-side parallel frame sections arranged to extend vertically relative to each other. Typically, these mast sections comprise opposed vertical extruded aluminum channels connected together by a plurality of cross pieces. With such construction, the mast sections are relatively heavy and relatively expensive to manufacture. The weight of a scaffold unit of this type is an important consideration since these units must be moved from place to place and loaded onto and off of trucks by the workmen using the scaffolds. The cost of construction is also an important consideration in enabling the scaffold units to be sold at a price that can be afforded by purchasers. The weight of the mast sections is, of course, also related to the cost of manufacture in that the more the weight, the more the material that is used in the mast.
The mast of the Ser. No. 781,221 application comprises a plurality of telescopically arranged aluminum extrusions. Again, such a mast is relatively heavy and expensive to manufacture. In particular, aluminum extrusions require costly dies for the extrusion process and the wall thickness of an extruded column must inherently be relatively great. The outermost mast sections in particular will have considerable weight and be quite high in manufacturing cost.
The main object of the present invention is to provide a pedestal type scaffold with a extendable mast which is much lighter in weight and more economical in manufacture than those of the prior art.